A carefully chosen selection
The good news about describing the world in terms of energy stores is that there are a limited number of stores to think about. Here is a selection of stores, with those that might be used earlier listed first. In each case that there is more of less energy in a store is a semi-quantitative description, standing in for a useful calculation that can be done.
Energy stores can be more or less full
Imagine a car travelling down the road, the amount of energy in the energy store (in this case a chemical store) decreases. As changes occur, it is often the case that energy stores are filled or emptied.
It is best not to think of a store as empty or full – just as augmented or depleted during processes. Augmenting and depleting stores may be a precise way of expressing matters, but we'd be surprised to find this language being useful in classrooms. So it is better to talk in terms of increasing or decreasing the energy in a store, of filling up and emptying the store.
Filling and emptying
You'll need to become familiar with these, paying particular attention to identifying physical clues in a process suggesting changes in the quantity of energy in a particular store.
- shifting energy to a chemical store: water and carbon dioxide rearranged to give sugars and oxygen
- shifting energy to a gravity store: water pumped uphill in a hydroelectric scheme
- shifting energy to a kinetic store: a cyclist speeding up as she sprints for the finish line
- shifting energy to a thermal store: a kettle warming water for a hot water bottle
- shifting energy to a thermal store: melting ice
- shifting energy to an elastic store: drawing back to the elastic on a bait catapult
- shifting energy to a vibration store: sea waves increasing their height as a storm passes, or a swing moving more and more as it is pushed
- shifting energy to a nuclear store: stellar reactions
- shifting energy to an electric or magnetic store: rubbing a comb against a woollen jumper, or pulling magnets apart
- shifting energy from a chemical store: petrol and oxygen combining to give water and carbon dioxide
- shifting energy from a gravity store: a meteorite falling towards the surface of a planet
- shifting energy from a kinetic store:A large tanker gradually coming to a halt as it drifts through the water with its engines off
- shifting energy from a kinetic store:
- shifting energy from a thermal store: a storage radiator cooling down
- shifting energy from a thermal store: steam turning to liquid water
- shifting energy from an elastic store: letting air out of your bike tire
- shifting energy from a vibration store: A wave driven generator providing power to the electrical grid
- shifting energy from a nuclear store: Fission reaction, where large nuclease split in power stations and bombs, or fusion reactions, where small nuclei join, such as within the Sun
- shifting energy from an electric or magnetic store store: electrons being fired towards the television screen, or allowing magnets to come together
Note that electric and magnetic stores are magneto-static and electro-static, so do not apply to electrical circuits.
A full set
Here are all of the stores on single sheets:
- Firstly, more empty, ready to be filled.
- Secondly, more full, ready to be emptied.
But how do you tell if the store is being filled or emptied during a process?